Selective signaling system



Nov. 24, 1931. w. 1 sHAFER SELECTIVE SIGNLINGrI SYSTEM Filed Feb. 25, 19.51

lil N Marinated Non M1, 1931 UNITED STATES PATENT oFFlcE y y mm L. BHAFEB, OF MOUNT LEBANON TOWNSHIP, ALLEGHENY COUNTY', Pm-

SYLVANI, ABSIGNOB TO AMERICAN TELEPHONE AND TELEGRAIPH COIPANY1-A 4 OOBPOBATION OF NEW YORK BELECTIV'E BIGNALING SYSTEM Application med Icbruary 25, 1931. Serial No. 518,267.

Thisinvention relates generally to signalsystems. More particularly, this invenu tion relates to devices and apparatus to be employedin connection with signaling sys-` ".1 tems of the selective type.

lt has heretofore been diicult under certain circumstances to transmit coded signals suitable to operate a commercial selector capable of closing a circuit coupled to the seio lector so as to energize an indicatin device connected to the coupled circuit. urther diculties were encountered as the coded signals took the form of direct current pulses occurring at low frequency and as the transmitting medium was a telephone line subiect to power induction from extraneous sources. These diiliculties become apparent when one realizes that ordinary telephone circuits are bridged by drainage coils which exhibit very low impedances to pulses of o ien cycles per second, i. e., 31/2 to 1.0 cycles per second, which are the ordinary limits of 4 operation ci the commercial selector. The low impedance of the drainage coils causes practically all of the low frequency coded current to become shunted from the telephone circuit and, therefore, the selector often tails to operate.

diculties,

v To overcome these and other rent and to produce pulses o alternating current spaced in accordance with the characteristie ci the commercial selector. 1t is another object of this invention that the frequency ci the alternating current besuch that the bridging leakage coils of the telephone circuit will exhibit high impedances so dll it is the object of this invention to. employ an; alternating current instead of a direct cur-- the selector would become energized upon th operation of the selector.

These and other objects of this invention become apparent from the detailed description hereinafter following when read in con-l nection with the accompanying drawings in which Figure 1 represents one embodiment of the invention given merely for the purose of illustration, and Fig. 2 shows a modi-` ned arrangement of part of the apparatus, shown in Fig. 1 so as to permit the simultaneous transmission of coded current an speech currents. .y

Referring to Fig.l lof the drawings, the reference character L represents a telephone'. g line capable of freely transmittin s h' currents. This line is bridged by amage coils K1 and K2. The line L is terminated at its left side by the secondary winding of an insulating transformer T1 and at its ri ht4 7 side by the primary windin of a simi r transformer T2. The win 'ngs of .both transformers T1 and T1 are insulated against high voltages of the order of 25,000 or 50,000 volts or more. The midpoints of the sec. 1| ondary winding of transformer T1, the primary winding of transformer T, and of the drainage coils K1 and K3 are all grounded, as shown.

The telephone line L may run parallel to n'.

a high voltage power circuit and, in facttit may be so exposed as to induce substantial` currents from extraneous sources. These extraneous effects will send currents through ing the circuits connected or coupled to thal' primary winding of transformer T1 as well as' to the secondary winding of the transformer T2. These protective features render the arrangement of this invention articularly adaptable for selective signalin tween sta- Il tions located along an electrifie railroad.

The primary winding of the transformer T1 extends to the armatures of a relay R1. One terminal of the windin of the relay R1 is connected to a grounded attery B1. The 100 amount of the current.

I Fwhich embodies peripherally arranged teeth spaced in some predetermined manner characteristic of a desired calling signal. The dial calling key may be manually revolved in one direction and then released so that it may revolve in the opposite direction and close the contact E1 a number of times at certain intervals determined by the spacing of the peri heral teeth. Current will then flow from the attery B1 through the winding oi the relay Rl during such time as the contact E1 is closed, and this current will, of course, be interrupted while the contact E1 is open. lt

- will be obvious that separate dial calling keys may be associated with the contacts E2 and E., and that these may be independently operated and that, moreover, a master calling key of any type well known in the art may be used to selectively close any one of the contacts El, E2 or E8, as found desirable.

The inner contacts associated with the armatures of the relay Rl are connected to an alternating current generator which may sup ply current of any frequency conveniently transmitted by the line L. Current of a frequency of 60 cycles is readily available in most places and its use is preferable in the arrangement of this invention because a frequency of that order is at or slightly below the lower limit of the ordinary range of audibility. Moreover, the impedance of the draina ge coils K1 and K2 is suiiciently high at 60 cycles so as not to by-pass an a preciable It will e understood., however, that current of a frequency above the range of audibility. i. e., 5,000 cycles or more, may be employed, if desired.

The outer contacts of the armatures'of the relay R1 extend to a telephone subset A1, which may be of any well known type. These outer contacts are normally closed and a telephone conversation may normally take place in opposite directions between the subset A1 and another sub-et A2 which may, if desired, be of the battery type and which is connected to the secondary winding of the transformer T@ through a pair of condensers C1 and C2. The telephone conversation will only be interrupted upon the operation of the relay R1 as a result of the closure of any one of the contacts El, E2 or Es4 by one of the teeth of the associated dial calling key.

The secondary winding of the transformer T2 is connected through a pair of retardation coils K3 and K4 to a full wave rectitying apparatus D, which may be any well known type, preferably of the copper oxide type. The rectifying apparatus D may include four copper oxide rectiiiers so related as to convert the alternating current transmitted over line L by the generator G into direct current.

raaaooe Each pulse of alternating current will produce a corresponding pulse of direct current'. The various pulses of direct current will flow through a sensitive direct current relay Bw, the armature of which will close its contact once for each pulse. It will be apparent that the relay R2 will follow the relay R, in synchronism.

The retardation coils K3 and IQ exhibit low im edances for all frequencies of the order o for exam le, 60 cycles. Their inpedance is high or ordinary speech frequencies; hence ordinary speech currents will be unable to reach the full wave rectifying apparatus D.

The armature of the relay RL controls a circuit which includes a battery B2 and a selector J. The selector receives the pulses of direct current determined by the movements of the armature of relay R2, and if these pulses of direct current are ofthe proper number and spaced in avpredetermined way in accordance with the setting of the selector, the selector will operate and close the circuit H. rlfhe selector may, of course, be of any type which will o crate in response to the reception of a code signal composed of a plu rality of direct current pulses spaced by predetermined intervals. One form of selector suitable for this purpose is described in a patent to J. C. Field No. 1,343,256 dated June l5, 1920. When the selector J operates, a bell will be rung or a lamp lighted, andv ot course, the operation of the Selector may be used to continuously energize any other well known form of visible or audible indicating device connected to the circuit H.

The circuit L0 and similar circuits may bridged across the telephone line L. circuitl bridging1 the line L may inclut transformer similar to the one. desi gnatcfl 'l as Well as all of the equi prnent shown in 'l of the drawings connected to the secondtuy winding of the transformer TL..

Fig. 2 shows a telephone sub-set fr con nected to the primary winding of the trans former T1 through a. pair of condenscrs C3 and C4. l-lerc a telephone conversation may becarried on continuously with any party connected to the telephone line even during code signaling operations. The lrelay El, when it is energized by direct current pulses, connects the generator G to the primary winding of the transformer T1 at the same time that the sub-set A is connected to that pri mary winding. Current supplied by the genn erator G will he transmitted over the teleA phone line simultaneously with the speech currents and the low frequency of the generated current Will not affect or distort the general wave shape of the speech currents.

Thus, it will be apparent that coded pulses of alternating current are transmitted over a telephone line and that the frequency of th's current does not interfere with the frequcn snit.

llt:

fainkin cies ordinarily resent in telephone conversations. These a ternating current pulses are converted into corresponding direct current ulses which operate one or more high speed irect current relays.

As stated hereinabove, the selector J is connected to the line L through a full wave rectifying device and a sensitive direct current relay. Commercial selectors-generally operate at frequencies of about 31/2 to 10 cycles; -cycle a ternating current will hardly affeet and operate these selectors. The inclusion of the full wave rectiying device and the sensitive direct current relay permit the roper use of these low frequency selectors or code signaling systems involving higher uenc currents. In connection with cerlector may be connected irectly to the rectifier without the sensitive direct current relay, andthe direct current pulses will then operate the magnets of the selector.

The code calling key orkeys and the various selectors permit selective signalin between diierent stations connected wit the same'line. One selector will be operated to the exclusion of all of the others, and the indicating device coupled to the operated selector will be energized to the exclusion of all other indicating devices coupled to the remaining selectors.

While this invention has been shown and described in certain particular arrangements' merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied forms without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is :l

1. The combination of a telephone line exposed to extraneous voltage effects, a plurality of telephone sub-sets connected to said line, a source of alternating current having a frequency close to or below the lower limit of the ordinary range of audibility, a toothed calling key, means responsive to the operation of said key to lconnect said source of alternating current to said line at intervals determined by the spacing of the teeth of said key, a full wave rectifier for converting the alternating current pulses into direct current pulses, and a selector responsive to said direct current pulses.

2. The combination of a telephone line, a plurality of telephone sub-sets connected to said line, a source of alternating current having a frequency below the ordinary range of andibility, apparatus for producing any one of a plurality of different codes, means responsive to the operation of said apparatus to connect said source of alternating current l to said line at predetermined intervals correspondlng to any one of said codes, a plurality of selectors each responsive to the direct curof lines, a pro erly designed se lli llll) 

